Significant neuroanatomical and neuromaturation changes take place during adolescence and are reflected n the maturation of abstract reasoning, affect, and cognition. Hence, exposure of millions of adolescent working children in developing countries to solvents might affect their cognitive and behavioral development, in a previous original study in Lebanon, we reported that male working children exposed to solvents performed worse on neurobehavioral assessment than non-exposed working children. The study had several imitations. The exposed children were recruited from 4 kinds of workplaces with variable solvent exposure. Exposure was assessed only once (4-hour passive monitoring) and a follow up study was not planned. This R21 application, a collaborative between the American University of Beirut (AUB) and the Oregon Health &Science University (OHSU), aims at building capacity at AUB and replicating the previous work towards ubmitting an R01 follow-up study. OHSU will bring in 30 years of experience in neurobehavioral research and their Behavioral Assessment and Research System (BARS) which was applied in different occupations, anguages, and age groups. A cohort of 100 male children (10-17 years) working in mechanics (exposed mainly to Methyl Ethyl Ketone and Toluene) and 100 male non-exposed working children will be recruited from a poor neighborhood in north Lebanon, in collaboration with the Center for Working Children in that neighborhood. The program has enrolled 68 working children in the past 18 months. The study will adapt BARS to the Lebanese context, pilot test it, train local researchers, and then use it to compare the performance of exposed to non-exposed children. The study will also develop a strategy to assess exposure of children to solvents using a combination of direct observation at work, passive air monitoring, and biological monitoring. The long-term goal is to submit an R01 application in which these children are followed-up for 3 years, whereby their exposure to solvents is carefully assessed, their neurobehavioral performance is retested in addition to a set of neurophysiological tests, and a functional MRI is performed on those with the worst exposure or performance. The R01 will address the controversial issues of long-term solvent neurotoxicity and the use of neurobehavioral testing as an early indicator of adverse neurotoxic effects. The findings will inform policy on child labor and solvent exposure.